Calculating your cholesterol ratio can provide useful information about your heart disease risk, but it isn't useful for deciding what treatment you should have to reduce your heart disease risk. Your total cholesterol and low-density lipoprotein (LDL, or "bad") cholesterol levels are more useful in guiding treatment than is your cholesterol ratio.
You can calculate your cholesterol ratio by dividing your high-density lipoprotein (HDL, or "good") cholesterol into your total cholesterol. For example, if your total cholesterol is 200 milligrams per deciliter (mg/dL) (5.2 millimoles per liter, or mmol/L) and your HDL cholesterol is 50 mg/dL (1.3 mmol/L), your cholesterol ratio is 4-to-1. According to the American Heart Association, the goal is to keep your cholesterol ratio 5-to-1 or lower. An optimum ratio is 3.5-to-1. A higher ratio indicates a higher risk of heart disease; a lower ratio indicates a lower risk.
For treatment purposes, it's important to know absolute numbers for all your cholesterol levels. People with very low HDL levels or very high LDL levels may be at substantial risk. There are effective ways to lower LDL cholesterol that are proven to reduce risk.